Improved Photodynamic Inactivation of Resistant <i>Nakaseomyces glabrata</i> Yeasts and Biofilms Mediated by ZnTE-2-PyP ⁴⁺ Porphyrin Combined with Silver Nanoparticles

<i>Nakaseomyces glabrata</i> is a high-priority fungal pathogen due to its incidence and antifungal resistance. Photodynamic inactivation (PDI) can offer a promising approach against resistant <i>N. glabrata</i>, particularly when the advantageous photophysical properties of Zn-(II) porphyrins can be enhanced by the plasmonic effect of metal nanoparticles (NPs). Herein, the association of ZnTE-2-PyP⁴⁺ porphyrin (ZnP-ethyl) with AgNPs (stabilized with polyvinylpyrrolidone, PVP) in PDI against yeasts and biofilms of resistant <i>N. glabrata</i> strains was investigated. AgNPs/ZnP-ethyl (NE) systems were prepared, and physicochemical characterizations indicated the interaction and spectral overlap between AgNPs and ZnP-ethyl, prerequisites for harnessing the plasmonic effect. Moreover, AgNPs had a minimal effect on ZnP-ethyl fluorescence lifetime. To investigate the role of AgNPs and strain susceptibility in PDI, yeast interactions with NE and ZnP-ethyl were assessed by fluorescence microscopy, which indicated that, in general, AgNPs facilitated the internalization of ZnP-ethyl by cells. Interestingly, HGV14 yeasts, which were unable to form biofilm, exhibited the lowest susceptibility to NE-PDI, likely due to reduced cell interaction relative to the other strains. PDI using ZnP-ethyl alone at 1.5 μM reduced HGV11 and HGV20 yeasts by 1 log₁₀, whereas NE-mediated PDI eradicated cells using 4-5-fold lower ZnP-ethyl concentrations. In biofilms, NE-PDI reduced the viability by ∼75% and induced high cell death to a much greater extent compared to other irradiated groups. Therefore, NE boosted the PDI of yeasts and biofilms across all resistant <i>N. glabrata</i> strains, likely driven by plasmonic effect and enhanced cell interaction promoted by PVP-AgNPs, making NE-PDI a promising strategy for combating resistant microorganisms.